Carbon-pile rheostat



H. BuMARSHALL CARBON 'PILE RHEOSTAT Filed Feb. 4,` 1924 lJune 23, 1925.1,543,083

Q@Wwhmllmlmiii|||||||li 33 sez disks.

Paimea .lune 23, 1925.

UNITED STATES v1,543,083 PATENT OFFICE.

HARRY B, MARSHALL, or sT. lLOUIS, MIssoURi.

CARBON-PILE RHEOSTAT.

Application filed February 4, 1924. Serial No. 690,428.

T01/ U whom it may concern: .f l

Be it known that I, HARRY B. )Loisir-xm.. citizen of the I'nited States,residing at St. Louis, '.\[issouri, have inventedfcertain new and usefulImprovements in a Carbon-Pile Rhcostat; and I do .lierebydeclare the foblowing to be a full, clear, and exact description of the invention, suchaswill enable others skilled in the art to which it apper- -tains tomake and use the saine.

My invention relates to rheostats of the general class in, which thevresistance is vai'ied b v compression, as for example by compressing apile of carbon resistance Viewed `in one invention aims to provide acheaply manufactured, compact and highly effective rheostat of thisgeneral type. aims to' provide an assembly adaptedvlto be supportedfrom4 one end and one wliicli',\\'ill have a large share of theoperating portions secui'elyf housed to guard against tampering withthesame. and aims to -provide a rlieosat partic- .ularly adapted for usewith relatively small l currents. i

In another iaspect, my invention aims to `provide a rheostatconstruction inl which a cheap and simple assembly will insure ade-lquate electricalconnections between various elements and also adequateinsulation where the same is needed. Furthermore, my 'invention aims toprovide a rheostat' assembly .Ill

in which a spring isemployed both' for. carrying the current to one endof the coinpressilile' resistance,for continuously maintaining apredetermined minimum pressure on tliis\.resistance. and for reducingthe efffect of the adjustable pressureroducing to provide simplemeansfor makingthe circuit connections to the resistancev unit; also fora'ording an indication which will readily permit a given compression ofthe resistance Ato be duplicated. 4It also proof its general aspects,my-

vides a rheostat which can readily be attached to'a siippoiting panel soas to be sup ported entirely from its head end. and one which iseffectively sealed to guard against tampering. Furthermore, niyinvention provides highly desirable kfeatures of construction andarrangement, together with other and more detailed objects will appearfrom the followingspecification and fromtlie accompanying drawings. Inthe drawlngsf f l Fig. l is a perspective view of a rheostat embodyingmy invention. f

Fig. Q V'is an enlarged central and longitudinal section through -thesame, showing this rheosat as attached to a supporting "wall, such as aportion of the front 4panel of a radio receiving outfit.

Fig. 3 is a central and longitudinal seetion through an embodimenthaving a somewhat different casing construction and a -v different formof presser block.

Fig. 4 is a-central and longitudinal section through still anotherembodiment, namely one including a shell of inciilating material.

Fig. 5 is a fragmentary section showing (in a somewhat exaggerated view)how the v compressible-thrust transmitting means comp nsate forirregularities in the dimensions oi. the elements which constitute theresistancejpile. e

In one of its immediate commercial embodiments, my `invention isparticularly adapteilfor embodiment in rheostats adapted to bek attachedto lthe panelsof radio rel ceiving sets and to be connected in serieswithA the battery .current for a vacuum tube. I am thereforeillustrating and describing my invention in such an embodiment, althoughI do not wish to be limitedto-the employment of any of its novelfeatures for an i particular commercial purpose. l

ieferring first to the embodiments of Figs. 1 and 2, these show a carbonpilerheostat having a metal casing in the form of a tube enlarged indiameter adjacent to its forward end so as to afford a cylindricalshank'portion 2 which extends through a correspondingbore in theinsulating panel 3 of the ra'dio receiving set or other appara tus inconnection with which the rheostat'is employed. vThis cylindricalshank.. portion 2 of the casing terminates in a head 4 adapted to hearagainst the forward face of the panel 3 so as to be clampedcagainst thelatand the head 4.is provided with a threaded.

bore axial ofthe casing for receiving-a coinpressing screw 6 whichnormally has its i pointed tip projecting, into the considerably ing 7,the forward endof this pile being en-V larger bore of the rear or mainportion of the metal casing. This mainbore portion of the casing isprovided with an insulating `linin here shown as consisting of aninsulating tube 7, aninsulating washer 8 at` the forward end of thebore, and an insulating bushing 9 which has its head disposed in therear end of the bore and which has a shank projecting through theerforated rear end 10 of the casing. xtending through the bore of thisshank of the bushing is the threaded stem 11 of a' metal thrustreceiving member which has its head 12 within the insulating lining ofthe` casing and engaging the head of the bushing 9.

Stacked against this thrust receiving member 12 is a pile of resistanceblocks 13, desirably in the'form of carbon disks of a size freelyfitting the bore of the insulating lingaged bythe head 14 of a presserblock, while another presser. block 15 has a forwardly directed headengaged by the 4pointed tip of the screw 6. Interposed between the headsof the presser blocks 14 and 15 is a compressed to a predetermin spiralcom ression sprin arlgle than the point of the screw, so that thispresser block may rock about the extreme tip of the screw ,in permittingthe presser block to tilt out'of axial alinement with the casing whencompensating for irregularities in the sha ing of the spring or' in thedimensions of t e stack of resistance blocks at various pointsperipherally of the latter after the -manner shown in Fig. 5.

To permit of such tilting, each ofy thev presser blocks 14 and 15 hasits head portion considerably smaller 'than the bore of the insulatinglining 7. Moreover, each of these presser blocks desirably has a shank,

portion freely entering the bore 'of the spring, the two shanks beingdirected towards each otherand 'these Shanks desirably are of such a'lenh that they will engage each other when t e s ring has been extent.

, To make the needed circuit connections to the two .ends of theresistance unit, I

desirably connect one side of the circuit to the stem 11 o f the thrustreceiving member 16 which springtransmitst e thrust of t e screw. over011e` carried to the forward end .of the resistance ile through thescrew 6, the presser -mem-v rs 14 and 15, andthe spring 16. For makingsuch circuit connections, Fig. 2 shows a terminal plate 17 having a boreinto which the shank of the insulating bushing 9 extends and havingaffacc portion bearing against the yrear end`10 of the metal casing, sothat one circuit wire 18 can be `fastened to this terminal plate` by abinding screw 19. The other circuit wiref 20 is clamped between a pairof lock nuts 21 and 22 which .are both threaded on the stem 11, the nurI21 being separated from the terminal plate 17 by an insulatinl washer23. With the parts thus arrange it will be evident that the' nut21simultaneously draws the head- 12 of-the thrust receiving member andthe bushing 9 rearwardly, and clamps the terminal late-17 between therear end 10 of the casing andthe insulating washer.l 23.

Inemploying such a carbon pilerheostat for purposes in which a givensetting of the rheostat may need to be duplicated, I desirably imbed theforward head 4f of the casing iny an insulating dial 24having suit-vable markings 25 disposed radially thereon. Then I desirably provide thescrew 6 with an insulating knob 26 havingvan indicating groove or line27 .extending longitudinally thereof, so that this line will cooperatewith the markings 25 on the dial in affording an approximate indicationof the setting o the rheostat. I also desirably make the screw of such alength that the rear Vface of the knob 26 will engage the front of thedial 24 to limit the extent to which the .screw can be moved in apressure exerting direction, thereby avoiding a possibleoverstraining ofthe arts which tis important `in a rheostat built in a rather small sizefor use by amateurs.

In manufacturin such a un'it, the main portion 1 of the casing initiallyhas its rear end o ning` of the full size/of its bore, so that t evarious elements normally housed by this bore can all be vinserted .fromthe rear end.- When this has been done, the

rear end of the original metal tube is 'spun over to form theVed-.flange10, thereby holding the contents of the tube securely in position so asto with the' same. unit can then. shipped with the nut 5, the terminalplate 17, insulatin washer-23 and the lock nuts reventan tam rin Ihre ype bg 120' 21 and 22 al detached, so. as to permit'the l readyinstallation of the casing through the bore in the insulating enel 2,after which the said. previous] etached parte can readily be assembleven by an amateur.4

However, while Fi `1 and 2 show an arrangement of the parte` .which Ihave found highly advantageous, I do not wish to be limited tothevarious featuresofconstruction and arrangementthus disclosed,

.it being obvious that the same might be engages the forward face of thepanel. The

same' figure also showsthe circuit connec- `ltions. as made through twoterminal plates 29 vand 30 spaced by an insulating washer 31 and bothclamped in position -by a single nut 39. threaded on the stem 1l rof therear presser member. In this case. the insulating lining is similar tothat of Fig. l, but the spring 1G is'shown as directly engaging theforward end of the resistance stack 13. Y

Fig. 4 shows still another embodiment, namely onein which an insulatingtube connects a pair ot tubular metal heads, so that the maintubularportioii 1 of the metal casing as eniployed in the embodiments ofFig. Q and Fig. 3 is notneeded. yIn this case .the resistance pile 13,the spring 16 andthe presser members 1l and 32 aie all housed by aninsulating tube 33 which -has thickened end portions all'ordingshouldcrsover which the mouth portions of the cup-shaped tube receivingparts of the two metal heads are spun inwardly. The forward metal headhas such a cupshaped portion of larger diameter than the `shank 35 ofthis head,

so as to afford a shoulder for clamping one circuit terminal plate 36against the rear of the insulating panel 3, while a nut 3T.'

threaded on this shankengages the front ofthe panel. wardly opencup-sliaped portion 38 clamped over thethickened rear ,endofthe'insulat# ing tube and has a rearwardlyv projecting threaded shankupon which the other circuit terminal' 39is clamped by a nut 40. Thisrear head also has another cup-shapedportion l1 extending .forwardlyinto the insu- 'latiiig tube for wedgingly receiving the" shank vof thethrust receiving member 42 so as to make the needed electricalconnection" to this member.

ll'ith 'the embodiments of Figs. 3 and 4, i

the rheostat is attached to theA panel by first inserting a portion fromthe rearofthe panel, but in each case the major portion of the unit issealed against tampering'and tlie'entir'e unit issupported from its for"ward end.

I claim as my invention 1. A rheo'stat comprising a pile of re sistanceelements, a screw lin axial alinem'ent The rear head has av for-.

with the pile, a compression spring operatively interposedibetween thescrew and the pile, andmeans operating'through the bore of the springfor limitingtbe compressing of ythe spring by the screw.

2. A rheostat as per claim 1, in which the said means comprise a pair ofpresser members khaving heads respectively, engaging the screws andthe'nearer end of the pile, and a spiral spring disposed between thelsaid heads, the presser hiembers having shanks rextending toward-eachother within the bore of the spring and adapted to engage each otherwhen thespring has been coin- .presscd toa predetermined extent.

3. A rheostat comprising as its sole sup? porting member a metal tubecontracted at both ends to al'foidperforate heads for the tube,"aninsulating lining for the tube comprising a tubular portion and av pairof perforate end portions respectively engaging the 'inner faces of thesaid heads, .a pile or resistance elementwithin the tubular p0rltion of'the insulatingT lining. a screw threadthe inner faces of the saidheads, 'a pile of resistance elements within the tubular portion of theinsulating lining, a screw threaded through one head, thrusttransmitting means disposed within the said tubular por-k tion andoperatively interposed between and electrically connecting the screw andoneend of the pile, a circuit terminal member having a portion engagingthe other end of the pile and having 'a shank projecting through theadjacent/head of the metal tube. a' second circuit terminal memberengaging the the last named head of the-metal tubc, and -meansinsulating the first named circuit terminal" member from the metal tubeand from the second terminal member.

5. For/use with asupporting panel provided with a perforation, a metaltubular member havinga main tul'iular portion insertible through thesaid perforation from the front of the panel and having at its for--wardend aV hea'd having a flange engaging the'front of the panelandhaving a thread ed bore smaller in diameter than the boreA 'i ofthesaidmain tubularportion. thereby providinga perforate forward end forthe said main'portion; the rear end of thesaid main portionbeing flangedinwardly to proill ,v'ide a v rfora'te rear end, insulating .means lininor the said main tubular portion and its saidperfora'teends, avresistance pile dis-l posed .within the said linin a terminal screwhaving a head dispose between the `rear .end of the said liningand theresistance pile and having a shank projecting throughthe said end,a'pair of circuit terminals removably su ported by the said shank, meansfor insu ating the said termi 'nals fromeach other and for insulatingone thereof from the said, shank and the other thereof from the saidhead, a screw thread- :tube provided with heads,

ed through the said bore of the forward head, thrust transmitting meansinterposed between the screw and the forward end of the resistancepile,V and means threaded upon the metal tubular member for ing theforward head thereof to the anel to afford a support for the entireappliance.

6. Afrheostat comprising a pile of resist- 'ance elements, a casinincluding a tubularguide portion of insu ating material housing the saidpile and having a rear insulating head portion adjacent to one end ofthe` pile, the Casin also having a forward'head,

`ra'screw threa ed through the forward head,

and a compression s ring between the screw and the forward en of thepile, circuit connections to the screw and the rear end of the. ile, andan insulating. element associat with the forward head for limiting theexpansion of the. spring when the screw 1s retracted to a certamextentand for interruptin the circuit when the screw isl retracted stillfurther. j

7, For use with apsupport having a vperforation therein, a rheostatspring and a compressible resistance disposed in tandem within the tube,one of the eads having a threaded shankextending through thesaidperforationand having a against the other face of-the sup portion ena 'ng one face of the support, a

nutv threa e 4on the shank and aring Port, a

screw extendin axially through the shank and arranged' or exerting. acom ressing pressure von the s pr and in eatin means. associated with te screw for indiv eating the adjustment thereof.

8.- For use with a support having a perforation. therein, a rheostatcomprising a tube provided with heads, 'a compression spring and .a comressible resistance dissed in tandem within the tube,.one of the pads'having athreaded -shank' extending n through the said perforation andhavinga clamppgojectin comprisingA a a compression .portion en a ing oneface of the support, a

on the shank and bearing nut threa e against the otherv face of thesupport, a

screw extending axially through the shank.

and arranged for exerting a compressin ressure on the spring, agraduated dia ast upon thenut, and means fast upon the screw foraffording an indication on the dial to indicate the adjustment of thescrew. 9. A rheostat as per claim 7, including means fast on the screwand adapted to engage thel dial to limit the pressure increasingmovement of the screi 10. A rheostat including a pile of resistancedisks, a screw in axial alinement with the said pile, a pair of presserblocks hav-' `ing oppositely directed portions respectively inginterengaging portions permitting a rocking of the, resser block aboutthe tip of the screw an the said presser block being smaller in diameterthan the bore of the insulating housing to Vpermit such rocking.

nsV

`12. A rheostat including an insulating tube, a stack of resistance ksin the rear portion thereof, a metal support for the in'- sulatin tube,the said supportaffording a forwar head for the tube, a screw threadedthrough the said head into thetube, a Y perforated insulatoradjacent tothe rear of.A -the head and throughwhich the screw normally extends, acompression sprin in the forward*a portion of the tube, a orward presserblockdisposed between the spring and tlie tip of the screw, and as rearresser block between the sprin and the sai stack, and circuitconnections eadin res ctiv'el to the rear end of the stack an to themeta sulpport; the springhaving such expansi-' b1 i ty as tol force theforward presser block against the said insulator when the screw issuiciently retracted, so that the circuit can be interrupted throughsuch retraction of thesscrev'. S I

i ne rat t. ouis Missouri February 1, 1954. U Y v HARRY n. MARsHALL.' e

